Gen~ wave loop playback bug or not?

Hello! I have a simple loop playback in gen~ using wave. Frequency of driving phasor calculates from start and end loop points. In my example end point = buffer size. When I change a starting point - there is noticible change in pitch (down) after about a half of buffer. And almost at the end it drops to zero. And at the very end it return to looping with high pitch. I made same patching using regular wave~ object - all works as expected, without pitch drop. What's wrong with my patch?